The present invention relates to a pilot-type two-port vacuum valve connected between a vacuum chamber and a vacuum pump and used for gradually reducing pressure in the vacuum chamber to vacuum pressure.
In general, if gas at atmospheric pressure or high pressure in a vacuum chamber is exhausted rapidly in reducing internal pressure of the vacuum chamber to vacuum pressure by a vacuum pump in a manufacturing process and the like of a semiconductor, a large amount of gas flows temporarily. As a result, gas turbulence occurs in the vacuum chamber, a cloud of particles deposited on a vacuum chamber inner wall or the like is raised, and the particles may be deposited on a workpiece or the workpiece moves and a set position of the workpiece may be displaced.
Therefore, a vacuum valve having a main valve body having a large flow path area and an auxiliary valve body having a small flow path area is disposed in a flow path connecting the vacuum chamber and the vacuum pump. As shown in FIG. 7, after carrying out initial exhausting by opening the auxiliary valve body with the small flow path area, the main valve body with the large flow path area is opened to thereby to thereby change a gas inhalation amount in stages.
However, because the flow path area of the main valve body was much greater than that of the auxiliary valve body, it was found that a sudden change in a flow rate occurred and that the gas turbulence was likely to occur in the vacuum chamber even if the main valve body was opened immediately after the auxiliary valve body had been opened to carry out the initial exhausting.
It is an object of the present invention to provide a pilot-type two-port vacuum valve in which a valve opening degree is gradually increased in opening of a main valve body to make change of a flow rate smooth to thereby prevent occurrence of gas turbulence in a vacuum chamber and to stably carry out exhausting.
To achieve the above object, according to the invention, there is provided a pilot-type two-port vacuum valve comprising: a chamber port to be connected to a vacuum chamber and a pump port to be connected to a vacuum pump; a casing including the ports; a main flow path having a large cross-sectional area and an auxiliary flow path having a smaller cross-sectional area than the main flow path for connecting the chamber port and the pump port in parallel; a main valve body for opening and closing a main valve seat in the main flow path and an auxiliary valve body for opening and closing an auxiliary valve seat in the auxiliary flow path; a first piston connected to the main valve body through a first shaft and a second piston connected to the auxiliary valve body through a second shaft; a main pressure operating chamber for applying air pressure in a valve-opening direction to the first piston and an auxiliary pressure operating chamber for applying air pressure in a valve-opening direction to the second piston; and first spring means for repulsing the main valve body in a valve-closing direction and second spring means for repulsing the auxiliary valve body in a valve-closing direction; wherein the main valve body includes a valve sealing member for coming in contact with and separating from the main valve seat to thereby open and close the main valve seat in a poppet manner and a pillar-shaped flow rate adjusting portion to be fitted in an inner hole of the main valve seat to move in the inner hole by opening and closing of the valve sealing member and the flow rate adjusting portion is formed in a gradually-tapered shape to thereby have a function of gradually increasing a flow rate of air flowing through the main flow path in opening of the valve sealing member.
In the vacuum valve of the invention having the above structure, in a case of exhausting gas from the vacuum chamber, after the auxiliary valve body is actuated by air pressure to open the auxiliary valve seat with a small flow path area to thereby carry out initial exhausting, the main valve body is actuated to open the main valve seat with a large flow path area to thereby carry out remaining exhausting, for example. At this time, the main valve body has the gradually-tapered pillar-shaped flow rate adjusting portion and the flow rate adjusting portion functions to gradually increase the flow rate of air flowing through the main flow path in opening of the main valve body. Therefore, generation of turbulence in the vacuum chamber due to rapid exhausting is prevented.
According to a concrete embodiment of the invention, the main valve body includes a locking portion having a larger diameter than the flow rate adjusting portion in a position extending from the flow rate adjusting portion, a stepped portion with and to which the locking portion is to be fitted and locked is formed in the inner hole of the main valve seat, and a valve-closing position of the main valve body is defined by the locking portion and the stepped portion.
The flow rate adjusting portion of the main valve body has a plurality of tapered faces with different gradients successively in an axial direction or is formed of a smooth curved face in a gradually-tapered shape.
According to another concrete embodiment of the invention, the auxiliary flow path and the auxiliary valve body are incorporated in the main valve body, the second piston and the auxiliary pressure operating chamber are incorporated in the first piston, the second shaft is incorporated in the first shaft, the main valve body includes a locking portion having a larger diameter than the flow rate adjusting portion in a position extending from the flow rate adjusting portion, a stepped portion with and to which the locking portion is to be fitted and locked is formed in the inner hole of the main valve seat, and a valve-closing position of the main valve body is defined by the locking portion and the stepped portion.
In this case, the first piston has a connecting hole for connecting the main pressure operating chamber and the auxiliary pressure operating chamber and the casing has one operating port for supplying pressure air to the main pressure operating chamber. It is also possible that the casing has first and second operating ports for individually supplying pressure air to the main pressure operating chamber and the auxiliary pressure operating chamber, that the first operating port communicates with the main pressure operating chamber through a through hole provided to the casing, and that the second operating port communicates with the auxiliary pressure operating chamber through a through hole provided in the casing and the first shaft.